Who Writes Faster: Mongo or Postgres? I Ran a 1M Record Experiment to Find Out

Hasan — Tue, 22 Apr 2025 10:25:21 +0000

🚀 I wanted to know: Which database inserts 1M records faster—MongoDB or PostgreSQL?

So I built a benchmark pipeline from scratch—and the results surprised me.

💡 Why I Built This

I've always loved both Mongo and Postgres. But when it comes to high-volume writes...

💭 Which one actually performs better?

To find out, I created a controlled benchmark:

Installed both on Docker locally
Used realistic e-commerce data
Ran single, batch, and concurrent insert tests
Collected performance data: insert speed, CPU, memory

🧪 Step 1: Generate Realistic Data

I used Python + Faker to simulate real-world e-commerce activity:

50,000 customers
50,000 products
900,000 orders

Each record includes nested objects, timestamps, and varied fields. Think: preferences, inventory, shipping, JSON blobs.

python data_generator.py --customers 50000 --products 50000 --orders 900000

🛠️ Step 2: Run the Benchmark

I tested 3 insertion styles for both Mongo and Postgres:

Single inserts – one record at a time
Batch inserts – 100 to 10,000 records per operation
Concurrent inserts – up to 8 threads with batching

Metrics collected:

🕐 Elapsed time
🔁 Records per second
🧠 CPU usage
📦 Memory usage

⚔️ What I Found

🚀 Overall Performance

Database	Avg Throughput (records/sec)
MongoDB	46,012
PostgreSQL	8,900

MongoDB was 5.17x faster on average.

📦 Batch Inserts (Customers)

MongoDB peaked at 78K/sec
PostgreSQL topped at 29K/sec

Batching unlocks massive gains for both—but Mongo scales faster.

🧵 Concurrent Inserts (Orders)

MongoDB: 38K → 110K/sec (with 8 threads)
PostgreSQL: 14.6K/sec (plateaus early)

Mongo loves parallelism. Postgres has limits here.

🔍 Single Inserts

PostgreSQL wins in single insert performance
Its row-level optimization outperforms Mongo’s write path

⚙️ Resource Usage

Postgres used less CPU & memory overall
Mongo burned hotter under concurrency

🧠 TL;DR: Who Wins?

Category	Winner
🏎️ Overall Speed	MongoDB
🎯 Single Inserts	PostgreSQL
📦 Batch Scaling	MongoDB
🧵 Concurrency Scaling	MongoDB
💡 Resource Efficiency	PostgreSQL

🔧 If you need blazing speed, go MongoDB.

🛡️ If you need strict schema & efficiency, go PostgreSQL.

🧪 Try It Yourself (GitHub Repo)

Want to run your own tests?

# Clone the project
git clone https://github.com/hassancs91/mongo-vs-postgres
cd mongo-vs-postgres-benchmark

# Start databases
docker run -d --name mongo -p 27017:27017 mongo
docker run -d --name postgres -e POSTGRES_PASSWORD=postgres -p 5432:5432 postgres

# Generate data
python data_generator.py --customers 50000 --products 50000 --orders 900000

# Run benchmarks
python benchmark.py --data-dir data --output-dir results --postgres-host localhost ...

# Generate report
python report_generator.py --results-dir results --output-file results/case_study_report.md --charts-dir results

📁 You’ll get:

JSON results
PNG charts
Full Markdown report

🔭 What I'm Testing Next

Complex query performance (joins, aggregations)
Updates and deletes
Mixed workloads (read + write)
10M+ record datasets

💬 Let’s Talk

Which database has performed better for you in real-world write-heavy apps?

Have you ever hit a scaling wall with one of them?

I'd love to hear your stories 👇

📥 Full report + visuals + code:

👉 https://github.com/hassancs91/mongo-vs-postgres

🧑‍💻 Happy benchmarking!

Forem: Hasan